Conventional street sweeping vehicles, which have been known for several decades, comprise either a tractor or a truck frame, and have a pair of counter-rotating brooms disposed one at each side of the street sweeping vehicle. These counter-rotating brooms sweep debris from the edges of a road, or the like, even from against a sidewalk curb, to underneath the central area of the street sweeping vehicle. An elongate drum-shaped sweeping brush is disposed at the rear of the street sweeping vehicle and rotates about a horizontal axis to sweep the debris on the road forwardly to an elevator that receives the debris and lifts the debris into a hopper for subsequent controlled dumping from the hopper. A pair of opposed left and right drag shoes laterally border the sweeping brush and elevator and all together define an interior compartment that substantially contains the debris swept by the sweeping brush, before the debris is lifted by the elevator.
In use, debris builds up in front of the sweeping brush to a height of about four inches, and also tends to accumulate along the interiorly facing side surface of the drag shoes. Accordingly, the build-up of debris at the ends of the sweeping brush where the drag shoes contact the sweeping brush, tends to be quite significant. It is therefore important that the drag shoes seal against the respective ends of the sweeping brush, or in other words leave no gap between the drag shoes and the sweeping brush, so as to preclude the passage of debris rearwardly through such a gap. It is universally common with conventional street sweeping vehicles to have debris escape from between the drag shoes and the sweeping brush. Any debris that does escape through such a gap between the drag shoes and the sweeping brush will be re-deposited on the road so as to form a trail behind the street sweeping vehicle, which is unacceptable.
Also, some of the debris that is swept by the sweeping brush is directly propelled at the area of contact between the drag shoes and the respective sides of the elevator. The rotational speed of such sweeping brushes is about 180 r.p.m., or so, which tends to create quite a vigourous sweeping action. Considering that build-up of debris at the sweeping brush is typically about four inches high, it is common for such sweeping brushes to create a cloud of debris and dust up to about two feet high with the debris and dust travelling at significant speeds forwardly towards the elevator. Accordingly, it is important that the drag shoes seal against the respective sides of the elevator, or in other words leave no gap between the drag shoes and the respective sides of the elevator, so as to preclude the debris from being propelled forwardly from the sweeping brush through such a potential gap. However, since drag shoes must move up and down to follow a roadway surface, it is very difficult for conventional drag shoes maintain a proper seal against the elevator, especially after the mounting bearings of the drag shoes are worn. Due to such lack of sealing of drag shoes against the respective sides of the elevator, it is universally common with conventional street sweeping vehicles to have debris escape from between the drag shoes and the elevator. Any debris that does escape through such a gap between the drag shoes and the respective sides of the elevator would be re-deposited on the road so as to form a trail behind the street sweeping vehicle, which is unacceptable.
As discussed briefly above, it is inevitable for bearings on the drag shoe mounting assembly to become considerably worn in less than about fifty hours of operation, which typically represents slightly over one week of use. Since it is generally not feasible to change mounting bearings each week or so, it is common for street sweeping vehicles to have worn bearings much of the time. Accordingly, most of the time, virtually all street sweeping vehicles have significant gaps between the drag shoes and the respective ends of the sweeping brush and between the drag shoes and the respective sides of the elevator, thus significantly increasing the amount of debris escaping from a street sweeping vehicle to be re-deposited on a road surface.